High-spin States Of The Odd-odd Nucleus ¹²⁰Sb And The Odd-A Nucleus ¹⁵⁵Tm

This thesis mainly focuses on the study of the high-spin states of two nuclei from different regions, including the odd-odd nucleus 120Sb near the Z= 50 magic number and the odd-A nucleus 155Tm in the rare-earth region.Excited states of nuclei near the Z= 50 magic number have exhibited a wealth of interesting physics, the excited valence nucleons outside the shell closure can form the single-particle structures (the corresponding shape of nuclei are nearly spherical or oblate), and the proton excitations across the Z= 50 shell gap can form the collective structures (the corresponding shape of nuclei are prolate), therefore the nuclei in this region usually exhibit the shape coexistence phenomenon, which is one of the interesting phenomena in nuclear structure. In addition, the high-spin isomers in this mass region have attracted a lot of attention.High-spin states in odd-odd 120Sb were populated via the 116Cd(7Li,3n)120Sb fusion-evaporation reaction with a beam energy of 34 MeV. A self-supporting 116Cd target of 2.5 mg/cm2 thickness was bombarded by the beam of 7Li from the HI-13 tandem accelerator at the China Institute of Atomic Energy (CIAE) in Beijing. The γ-γ coincidence measurement was carried out using an array consisting of 9 Compton-suppressed HPGe detectors, one Compton-suppressed Clover detector and two low-energy photon spectrometer (LEPS) detectors.After detailed analysis of the experimental data, a total of 15 new γ rays were added into the level scheme of 120Sb. Based on the systematic comparison of single-particle levels between 120Sb and the corresponding core nucleus 118Sn, we have assigned the configurations of single-particle states in 120Sb, and most of these single-particle states in 120Sb can be described by the odd proton and the odd neutron coupled to the various excited sates in 118Sn. Based on the systematic comparison of isomers 120Sb and 118Sn, we proposed a new high-spin isomer in 120Sb, the configuration-fixed constrained triaxial relativistic mean-field (RMF) approaches were employed for analysis of the high-spin isomers in 120Sb, the calculated results show that these high-spin isomers have near-oblate shapes, the observation of a number of irregular levels decaying from these high-spin isomers indicates that these high-spin isomers should be the noncollective oblate. For the strongly coupled rotational band, we have extracted the experimental B(M1)/B(E2) ratios for the πg9/2-1(?) vh11/2 band in 120Sb for the first time, and made a systematic comparison for the experimental B(M1)/B(E2) ratios in 112,114,116,118,120Sb The experimental B(M1)/B(E2) ratios exhibit an overall decrease as the neutron number increases. In order to explore the origin of this decrease trend, the particle rotor model (PRM) calculations were performed. The calculated B(Ml)/B(E2) ratios exhibit an overall decrease with the neutron Fermi level changing from the bottom to top of the vh11/2 intruder subshell, which is consistent with the trend of the experimental B(M1)/B(E2) ratios. Therefore, the decrease of experimental B(M1)/B(E2) ratios as the neutron number increases may result from the different Fermi level positions of neutron in the vh11/2 subshell.Excited states of nuclei near the semi-magic nucleus 146Gd(Z=64,N=82) have exhibited a wealth of interesting phenomena, such as shape coexistence (near spherical, oblate, prolate and triaxial shapes), shape evolution (the shape evolu-tion of one nucleus with the increasing angular momentum, the shape evolution of isotopes or isotones), superdeformed bands, magnetic rotational bands, et al., thus the study of nuclei in this mass region is also a hot topic in nuclear structure.High-spin states in the nucleus 155Tm were populated via the 144Sm(16O, 1p4n)155Tm fusion-evaporation reaction at a beam energy of 118 MeV. The beam was delivered by the separated sector cyclotron (SSC) at iThemba LABS, South Africa. The target was 2.89 mg/cm2 thick with a backing of 13.13 mg/cm2 Pb. Deexcitation gamma rays were detected using the AFRODITE array consisting of 8 Compton-suppressed Clover detectors.After analysis of the coincident experimental data, we have clarified the dif-ferences between the reported level schemes of 155Tm, and a total of 27 new γ rays have been added into the level scheme of 155Tm. In order to explore the nature of the ground state band in 155Tm, we have plotted the E-GOS (E-Gamma Over Spin), and made a comparison with the neighboring odd-A isotones(isotopes), suggesting that the ground state band changes from vibration to rotation with the increasing angular momentum, the calculated results of Tilted Axis Cranking Model indicate that this transition probably comes from the excitation of neu-trons. Based on the systematic comparison, the yrast 25/2- state is proposed to be a seniority inverted state, clarifying the origin of this state. Multiparticle excitations in 155Tm mainly come from the alignment of valence nucleons outside the 146Gd core, when the full alignment of the 9 valence nucleons take place, the maximum angular momentum is 69/2 h, which is just the highest spin of the observed states in the present experiment.